Power clamps are known of the type in which a fluid motor actuated reciprocating movement is adapted to be translated into a swinging movement of a clamp arm attached by an additional linkage or other force transmitting means to the end of a piston rod of the fluid motor. Normally, in the retracted position of the fluid motor, the clamp is in the released position. That is, the clamp is removed from the work supporting surface and by means of fluid pressure the clamp arm is pivotally moved into operating, i.e. clamping position, to clamp a workpiece, such as sheet metal, to a work supporting surface and securely holding the workpiece there by means of fluid pressure in the fluid motor. Unfortunately, the high forces often developed during clamping along with misalignment of part contoured contact blocks (NC blocks), can damage critical part surfaces, and metal position during clamping can dramatically affect geometry of finished weldment, especially in the case of automotive body-in-white sub-assemblies, and consequently, final assembly.
In particular applications, such as automotive or aerospace applications, the skin or outer surface of a workpiece is required to be smooth and free of any undesired indentations or defects. Therefore, the conventional high contact force clamp devices do not provide an acceptable solution to concerns associated with a particular industry.
Therefore, it is highly desirable to have a clamp device and a means for using it for overcoming the problems associated with the high pressure contacts of the known clamp device. It is desirable to have a clamp device that controls shifting of the workpiece during assembly operations while at the same time protecting the workpiece from undesirable indentations or defects upon its surface. Finally, it is highly desirable to have a clamp device with an accurate and inexpensive means of identifying and adjusting clamp force during the assembly process.